This lecture introduces the concept of rigid body mechanics, emphasizing the need to consider the spatial mass distribution for solids in motion. It covers the definition of a solid's position using independent coordinates, the derivation of velocity for any point on the solid, and the calculation of acceleration. The instructor explains the importance of understanding the motion of a solid relative to an inertial reference frame, detailing the evolution of a solid in a reference frame and the formulas for angular velocity. The lecture concludes with the formula for the acceleration of any point on the solid, highlighting the implications of the assumption of a rigid body on the terms in the acceleration formula.